Should we trigger the ajax blur event when focusing a focusable element inside the drop-down list?
When a focusable element inside the drop-down list receives focus, the main text field loses it, and if an ajax blur event is registered, we could either fire it or not. If we do, this would cause a request, which in turn could cause a page update and closing the list while the user may be actually intending to interact with the focusable element inside the list. So, I would say no, we shouldn't fire it in this situation, but it's still subject to discussion.

Committed fix at revision 35875. Added a check on the click event to see if a focusable element triggered the event (or some other element contained by a focusable element like an link or a button) and in such case prevent selecting the item, which in turn prevents sending a request to the server and hiding the list.

Focusing an element inside the list will NOT trigger an ajax blur request (if defined).

Applied the same fix to ace:autoCompleteEntry and ace:selectMenu at revision 35883.

Committed another fix at revision 35889. When focusing an inner element, the drop-down list stayed open when clicking outside of the list and of the main text field of the component. So, this fix is to hide the drop-down list when a focusable element inside of it is blurred by focusing another element outside this component.

Confirmed EE 3.3.0 GA Build 13